The present invention herein relates to an electronic device, and more particularly, to a power amplifier having a depletion mode high electron mobility transistor (HEMT).
In general, a microwave integrated circuit (MIC) provided with a plurality of amplification transistors is included in a mobile repeater or the like processing microwave signals. The MIC for power amplification amplifies a microwave signal received from an outside and outputs the amplified microwave signal. In particular, for power amplification, a high electron mobility transistor (HEMT) may be used in a microwave band up to about 70 GHz.
The HEMT, which is a compound semiconductor device, has superior electron speed characteristics compared with a silicon device. Therefore, the HEMT is widely applied to a microwave or millimeter wave band (10-100 GHz) device. The HEMT device has advantages that the operation frequency is highest among field effect transistors (FETs) and microwave noise is low. Therefore, HEMT device technologies are being applied in developing a high performance wireless communication circuit operating in a millimeter wave band or an optical communication component having a bit rate beyond several tens Gbps.
HEMTs are classified into a depletion mode (D-mode) HEMT the threshold voltage of which has a negative value, and an enhancement mode HEMT the threshold voltage of which has a positive value. The D-mode HEMT is generally used for the MIC.
For stable operation of the D-mode HEMT, a negative voltage power source should be connected to a gate to which an RF signal is inputted. The D-mode HEMT stably operates without being floated when a negative voltage power source is provided. Also, the D-mode HEMT should be provided with a separate matching circuit so as to obtain matching characteristics in a specific frequency band. However, in order to provide a separate direct current bias circuit such as a negative voltage power source and a matching circuit to the gate of the D-mode HEMT, an additional cost is taken.